Objective To investigate the influence of smoking on fractional exhaled nitric oxide (FeNO) and small airway function in patients with chronic cough.
Methods A total of 205 patients with chronic cough who attended the outpatient service of Department of Respiration from May 2017 to June 2018 were collected as subjects. According to smoking or not, the subjects were divided into smoking group with 63 patients, never smoking group with 95 patients, and smoking cessation group with 47 patients. FeNO was measured for all patients, and the function parameters of small airway and FeNO values were compared among the three groups. The correlation between small airway function parameters and FeNO was analyzed for each group.
Results Compared with the never smoking group, the smoking group had significantly lower percentages of mean flow at 75%, 50%, 25% expiratory volume in the predicted value (FEF75%pred, FEF50%pred, and FEF25%pred, respectively) and maximal mid-expiratory flow (MMEF) at 25%~75% of forced exhalation volume (F=2.83, 2.74, 3.54, and 3.84, P=0.027, 0.031, 0.026, and 0.028); the smoking group had significantly lower FEF75%pred and MMEF than the smoking cessation group (F=3.05, P=0.046) and a significantly lower FeNO than the never smoking group (F=4.22, P=0.025). There was no significant correlation between FeNO and small airway function parameters in smoking patients (P>0.05), while FeNO was negatively correlated with small airway function parameters (FEF25%pred and MMEF) in non-smokers (r=-0.52 and -0.49, P=0.021 and 0.036) and the patients with smoking cessation (r=-0.54 and -0.02, P=0.003 and 0.029).
Conclusion Patients with chronic cough have significant reductions in small airway function parameters and a reduction in FeNO by smoking.
DownLoad: